In recent years, optical semiconductor devices including a combination of an optical semiconductor element such as an LED (Light Emitting Diode) and a fluorescent substance have grown in demand and found various applications including an outdoor display, a portable liquid crystal backlight, and automotive applications, because of their advantages such as high energy efficiency and long life. As LED devices have had increased brightness accordingly, the junction temperature has been increased because of increase in the quantity of heat emitted from the elements, or optical energy itself has been increased, which causes the problem of degradation of device materials. In recent years, therefore, development of device materials resistant to thermal degradation and photo-degradation has been awaited.
Japanese Patent Application Laid-Open (JP-A) No. 2006-140207 discloses an optical semiconductor element mounting board having good light reflection characteristics even after a heat test. Typically, as in the disclosure, a conventional thermosetting light-reflecting resin composition used as a board material often contains a release agent that has been added into the resin composition so that the board can be released smoothly from the mold in the process of manufacturing the board. In many cases, however, most compounds used as release agents are not compatible with based resin including epoxy resin, a curing agent and so on, which form a thermosetting light-reflecting resin composition. Therefore, when a board is formed by molding a resin composition containing such a release agent, the board is more likely to have poor appearance due to insufficient dispersion of the release agent, and this tends to make continuous molding difficult. Particularly, when an LED package is produced, a mold shaped to have a recessed part corresponding to an optical semiconductor element mounting region is used, and therefore, the flow behavior of the resin charged into the mold may vary greatly depending on the position. The flow behavior as well as insufficient dispersion of the release agent gives rise to destruction of the package or the poor appearance of the package.
A release agent and a dispersing agent optionally used together with the release agent are often thermally-unstable organic compounds. For example, therefore, when used for a long time under high temperature conditions or when exposed to high-temperature heating or used for optical semiconductor devices, a resin composition containing such compounds tends to be colored or have a reduced diffuse reflectance, so that it may tend to be difficult to obtain sufficient optical properties or reliability. Therefore, there has been a demand for development of a thermosetting light-reflecting resin composition having a high level of various molding characteristics such as releasability and also having good optical properties as well as high thermal discoloration resistance.
Patent Document 1: JP-A No. 2006-140207